The present invention disclosed herein relates to a nano-scale LED electrode assembly and a method for manufacturing the same, and more particularly, to a nano-scale LED electrode assembly in which a nano-scale LED device having a nano unit is connected to a nano-scale electrode without causing defects such as an electrical short-circuit while maximizing light extraction efficiency and a method for manufacturing the same.
The development of light emitting diodes (LEDs) has been actively promoted by succeeding in combination of a high-quality single-crystal gallium nitride (GaN) semiconductor by applying a low-temperature GaN compound buffer layer, by Nakamura et al., at Nichia Chemical Corporation in Japan, 1992. Such an LED is a semiconductor having a structure in which an n-type semiconductor crystal having a plurality of carriers, i.e., electrons and a p-type semiconductor crystal having a plurality of carrier, i.e., holes are junctioned to each other by using characteristics of a compound semiconductor, that is to say, a semiconductor device that converts an electrical signal into light having a wavelength band on a desired region to emit the light.
The LED semiconductor is called a revolution of light as a green material because the LED semiconductor has very low energy consumption due to high light conversion efficiency and is semi-permanent in the lifespan and environmentally friendly. Recently, as compound semiconductor technologies are developed, red, orange, green, blue, and white LEDs having high brightness have been developed. Also, the LEDs are being applied to various fields such as traffic lights, mobile phones, headlights for vehicles, outdoor electronic display boards, LED backlight units, and indoor/outdoor lightings, and also studies on the LEDs are being actively carried out. Particularly, a GaN-based compound semiconductor having a wide band gap may be a material that is used for manufacturing LED semiconductors which emit green and blue light and ultraviolet rays. Here, since a white LED device is manufactured by using a blue LED device, many studies with respect to the manufacture of the white LED device using the blue LED device are being carried out.
Also, due to the utilization of the LED semiconductor in various fields and studies on the LED semiconductor, an LED semiconductor having high output is required, and it is very important to improve efficiency of the LED semiconductor. However, it is difficult to manufacture the blue LED device having high efficiency. Drawbacks in improvement of efficiency of the blue LED device may cause the difficulty in manufacturing and a high refractive index between the manufactured LED and the GaN-based semiconductor. First, the difficulty in the manufacturing may be caused due to the difficulty in manufacturing of a substrate having the same lattice constant as the GaN-based semiconductor. A GaN epitaxial layer formed on the substrate may have many defects when the lattice constant with the substrate is significantly mismatched to deteriorate efficiency and reduce performance.
Next, light emitted from an active layer of the LED may not be escaped to the outside, but be totally reflected to the inside of the LED due to the high refractive index between the GaN-based semiconductor of the blue LED and the atmosphere. The totally reflected light may be reabsorbed to the inside to deteriorate the efficiency of the LED. The efficiency may be called light extraction efficiency of the LED device. To solve the above-described limitation, many studies are being carried out.
To utilize the LED device as lightings and displays, an LED device and an electrode for applying power to the LED device are required. Also, various studies on an arrangement of the LED device and two electrodes different from each other in connection with application purpose, reduction of a space occupied by the electrode, or a manufacturing method.
Studies relating to the arrangement of the LED device and the electrode may be classified into growth of the LED device and an arrangement of the electrode after the LED device is separately grown.
First, in studies on the growth of the LED device on the electrode, there is a bottom-up method in which the LED device and the electrode are formed and arranged at the same time through a series of manufacturing processes by using a method in which a lower electrode is formed on a substrate in the form of a thin film, and an n-type semiconductor layer, an active layer, a p-type semiconductor layer, and an upper electrode are successively stacked on the lower electrode and then etched, or the previously stacked are etched before the upper electrode is stacked and then the upper electrode is stacked.
Next, a method in an electrode is disposed after an LED device is separately and independently grown may be a method in which LED devices that are independently grown and manufactured through separate processes are disposed one by one on a patterned electrode.
The former method may have a limitation in that it is very difficult to crystallographically grow of high crystalline/high efficiency thin film and LED device, and the latter method may have a limitation in that light extraction efficiency is reduced to deteriorate light emitting efficiency.
Also, according to the latter method, although a three-dimensional LED device is connected to the electrode in a stand-up state in case of the general LED device, it is very difficult to stand up on the electrode in case of a nano-scale LED device having a nano unit. Korean Patent Application No. 2011-0040174 by the inventor of this application discloses a coupling link for easily coupling a nano-scale LED device having a nano unit to electrodes in a state where the LED device three-dimensionally stands up. However, it is very difficult to couple the nano-scale LED device to the electrode in the three-dimensionally stand-up state.
Furthermore, the LED devices that are independently manufactured have to be disposed one by one on the electrodes. However, in case of the nano-scale LED device, it is very difficult to respectively locate the LED devices on two nano-scale electrodes different from each other within a desired range. Also, even though the LED devices are disposed on the two nano-scale electrodes, defects such as electrical short-circuit between the electrode and the nano-scale LED may frequently occur, and it may be difficult to realize the desired electrode assembly.
A structure of an address electrode line for an LED module and a method for manufacturing the same are disclosed in Korean Patent Application No. 2010-0042321. In case of this application, a lower electrode is formed on a substrate in the form of a thin film, and an insulation layer and an upper electrode are successively stacked on the lower electrode and then etched to manufacture the electrode line. Then, an LED chip is mounted on the upper electrode. However, if the mounted LED chip has a nano size, it may be very difficult to accurately mount the three-dimensional LED chip on the upper electrode. Also, even though the LED chip is mounted on the upper electrode, it may be very difficult to connect the mounted LED chip having the nano size to the lower electrode. In addition, since n-type and p-type semiconductor layers of the mounted LED chip form upper and lower layers with respect to a substrate, light emitted from the active layer may be blocked by the LED chip and thus may not be escaped, but be absorbed to the inside, thereby deteriorating light extraction efficiency.